Determination of matrix flow units in naturally fractured reservoirs

The integration of capillary pressures and Pickett plots has been shown recently to be a useful approach for determining flow units. The present study extends the method to the case of naturally fractured reservoirs by preparing Pickett plots for only the matrix. This requires calculation of matrix porosities and true resistivities for the matrix. By placing pore throat apertures, capillary pressures and heights above the free water table on Pickett plots, it is possible to generate matrix flow units and to estimate if the matrix will contribute to production. Pattern recognition is the key to success with this approach. Two examples are presented. If total porosities and resistivities of the composite system are used on a Pickett plot when the partitioning coefficient (v) is constant, then the usual straight lines for fixed values of water saturation are not obtained. In this case, the Pickett plot results in downward concave lines. Not recognizing this effect might lead to significant errors in the calculation of water saturation.